This invention relates to printing apparatus and, more particularly, to printing apparatus of the type including a supply of printing material and a drive assembly coupled to the printing material and capable when enabled of advancing the material along a predetermined path past a printing station.
Printing apparatus of the above-described type have been known and used for decades, such as in the ordinary conventional typewriter, as well as, and more recently, in computer output printers and so-called "word-processing" systems. An example of a computer output printer is the Diablo HyType II Printer manufactured by Diablo Systems, Inc. of Hayward, Calif., and an example of a word-processing system is the Xerox 800 Electronic Typing System manufactured by the Xerox Corporation of Dallas, Tex.
Contemporary computer output printers and word-processing systems generally utilize a ribbon cartridge which houses a printing ribbon and has a drive mechanism connectable to an external drive source for advancing the ribbon along a predetermined path past a printing station located exteriorily of the cartridge. The cartridge may either be of the reel-to-reel type, such as disclosed in copending U.S. application Ser. No. 633,530 filed on Nov. 19, 1975 in the names of Mario G. Plaza and Richard D. Trezise and assigned to the assignee of the present invention (now U.S. Pat. No. 4,034,935), or the endless-loop type, such as disclosed in copending U.S. application Ser. No. 689,429 filed on May 24, 1976 in the names of Richard D. Trezise and Kip E. Nelson and also assigned to the assignee of the present invention (now abandoned).
It has previously been the practice in the case of reel-to-reel ribbon cartridges as used in a printing apparatus of the type above-described to incorporate some detectable indicia on the ribbon adjacent the end thereof on the supply reel in order to detect when the ribbon supply is about to be depleted. Typically, this indicia may include a strip of either reflective, transmissive or magnetically-sensitized material. Then, a suitable photo-electric or magnetic detection device at an appropriate location adjacent the path of movement of the ribbon could generate a RIBBON-OUT signal when the indicia is detected. Appropriate control circuitry in the printing apparatus would normally respond to such signal in a manner disabling further printing until a new cartridge has been inserted.
Although this approach has worked well in detecting the end of a fixed length of ribbon, it would not prove useful in the case of an endless loop ribbon. Further, in either types of ribbon cartridges, there would be no means of detecting either when the ribbon is not being advanced at all, due to a jam, broken ribbon, or failure of the cartridge drive mechanism, or when the ribbon is not being advanced fast enough, such as when it is slipping relative to its drive mechanism, or when the ribbon is not even present, such as when a ribbon cartridge has not been loaded into the printer.
It would be desirable, therefore, to provide in a printing apparatus of the type above-described an effective means for detecting the non-advancement, slippage or absence of a printing material regardless of whether it is of the endless-loop type or fixed length type, such as in the case of a reel-to-reel assembly.